Communications networks such as the Internet are used for transmitting information, e.g., digital data, from one device to another. Each communications network normally comprises a plurality of nodes, implemented using, e.g., routers, which are inter-connected by links over which data and control signals can pass. For ownership and administrative purposes, routers are frequently grouped together into sub-networks. Individual sub-networks which are made up of components which can be managed by a common administrator are sometimes referred to as an autonomous systems (“AS”). ASs may interact with one another to form much larger networks.
Internet service providers (ISPS) frequently implement one or more ASs. Each ISP is normally responsible for administering the AS which it owns and implements. The Internet comprises multiple ASs which interact with one another. As the amount of Internet traffic has grown, ISPs have been confronted with the problem of having to transmit ever increasing amounts of data over networks having an ever increasing number of nodes. In addition to being confronted with ever increasing amounts of traffic, ISPs continue to confront cost pressures which make it important to use network capacity in an efficient manner.
In older systems which relied on the Internet Gateway Protocol (IGP) for routing, the routing of packets was left to individual routers which would select the next hop, e.g., route to the next node, to be used to reach a destination based on a least cost, e.g., shortest path first (SPF), algorithm. The SPF algorithm was normally applied to a set of network information obtained from a plurality of broadcast messages including network topology information. The label distribution protocol (LDP) is a protocol that is normally used in non-traffic-engineered applications where the IGP determines the routing to be used.
Allowing individual routers along a communications path to determine routing by selecting the next router to be used reduces administrative complexity. However, it tends to result in routers along the shortest path between high traffic routers to become congested while other routers may become under utilized.
In recent years, in order to use network components efficiently, ISPs have begun to rely on traffic engineering. Traffic engineering allows administrators to explicitly control the flow of traffic through a network. Thus specific routes, e.g., paths, or portions of routes, can be established for the flow of traffic between various routers. Thus, in a traffic engineered system a router at the edge of an AS can specify the path which is to be used for specific data, e.g., IP packets with a particular destination address, through the AS. Since the full path through the network can be specified, data between nodes may be made to flow along routes other than the route that would be determined using a shortest path first routing algorithm.
In order to support traffic engineering, route establishment protocols such as the Resource ReSerVation Protocol (RSVP) are frequently used to establish paths through an AS. RSVP path establishment messages are transmitted along the path being established and are not broadcast to all routers in an AS.
For numerous reasons, ISP providers have chosen to implement individual ASs by using either LDP or RSVP throughout the AS but not both. In many modern systems where the benefits of traffic engineering are desired, this means that RSVP and not LDP is used for purposes of distributing routing, e.g., path, information.
Given that there are different and distinct benefits to using the LDP and RSVP protocols, it would be desirable to be able to selectively implement LDP and RSVP in different portions of a single AS. In some cases, it would also be desirable to simultaneously implement LDP and RSVP on the same router.